This invention relates to a process for the production of a polyester and to a novel copolyester obtained by the process.
It is known to produce a polyester by ring-opening polymerization of .epsilon.-caprolactone using ethylene glycol as a polymerization initiator. One problem of this method is that the molecular weight of the polyester is only about 5,000. Use of an organometallic catalyst has led to a success in obtaining a polyester having a high molecular weight of 100,000 or more. In order to use the polyester thus obtained for application as a biodegradable polymer, it is important to remove the catalyst completely so that the polyester is free of the catalyst.
A method has been proposed to use boron trifluoride diethyl etherate as a catalyst for the production of a copolyester of .beta.-propiolactone and .gamma.-butyrolactone (Urakawa et al, Polymer Preprints, Japan 42, 3721(1993)). This method, however, has a problem because the number average molecular weight of the copolyester is only 840-4,250 and because the amount of .gamma.-butyrolactone in the copolyester is 56 mole % at maximum.